You should never agree to sign anything you don't understand. Just ask politely to have an English version of the contract. If they won't do this, which is a Turkish legal requirement under Labour Law, just pass on the offer.

I have always trusted my employer and signed everything that was put in front of me. Now it seems that 1500tl extra "a bank promotion" was added to my pay (just once) and if I leave the university before 3 years I must return that money. I was told that I signed a document to that effect. When I asked for a copy of the document, I was told that it's too late, I should have copied it when I signed it. I checked my bank statement, the extra money was added.

Bank promotion??? Was this a payment because your employer changed banks? If so, the money was paid by the bank and I'm not sure that your employer can claim it back...whatever you signed. If you work at a university, take a walk over to the Law Faculty and find a friendly lawyer to ask for nothing...they are usually very helpful